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highfieldrebel 10th October 2011 06:17 PM

Novice build of Silbury
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I was looking for a speaker project so I could learn a bit about carpentry and after some interaction with Scott Lindgren, I decided to give Silbury a go, though I was a bit trepidatious. Silbury is a "Double-mouth back-horn with Olson style manifold-expansion named for Neolithic British sites", plans and support are available from Scott at I found very little about these speakers on the web and it definitely wasn't as difficult as I had feared, so I decided to post a few pictures to encourage others of similar skills to consider it.

I should mention that there is another thread on a similarish build where you can see how a skilled carpenter approached the challenge It should be redundant for me to state that no similar skills are contained in these posts, but I did learn a quite a bit and the techniques deployed by ArtsyAllen no longer seem like evidence of alien interaction.

I've attached a picture from the website of Silbury, it's about 6 foot tall and has a nice swooping back that apparently is important sonically, but I think it deserves to be in there for looks alone.

Silbury uses the MarkAudio 10.2 driver, the centre front is a compression chamber and then there is a horn section behind for more of that enjoyable bass. Construction wise the front, top, bottom and sides appeared easy to glue and clamp together (if I bought enough clamps). However, the vertical boards that form the back and the two internal walls seemed to me much less obvious.

highfieldrebel 10th October 2011 06:45 PM

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I'll come back to the internal walls in a while, first I'll describe making the curved back. If you're also inexperienced at woodworking, you should have the cutting done for you. My local B&Q doesn't stock Baltic Birch as the demand is so low, I eventually found a cabinet maker who would do the cutting for me on his table saw, I was really impressed with the accuracy. The cost was not for the faint hearted (180 for three sheets of 2440x1220 of 18 mm BB, another 50 for material collection and cutting. Ouch. Drivers were 99 each.)

One method mentioned elsewhere for a curved back is to draw your curve, jigsaw as close as you dare and then get sanding. This did not sound like fun, especially as I live in an apartment so lots of fine dust is not on.

I used a wood router and a stencil instead, it produces a lot small shavings, but they fall to the ground and are easy to hoover up.

I calculated the points of the curve every 100 mm and marked them on the piece of 9 mm thick MDF I was going to use as a stencil. Then I got a piece of 20 x 10 mm^2 pine and screwed it down to the MDF, bending the wood at each step so it matched the calculated points. This thickness of wood just about bent sufficiently, and was thick enough to pass screws through. I used a jigsaw to get close to the guide and then used a flush trim bit on the router to make it smooth. Next step is to duplicate the stencil, one lesson I learned on the project is that if your attention wanders while using a router it will take its chance to wreak non-reversible havoc upon your precious wood. I kept hitting crtl-Z but no good.

I found beginning a pass through the wood tricky, I'm not sure what I should have done differently, once the router gets going along the stencil though, it's plain sailing. Sand the edges afterwards and the curves are done.

sreten 10th October 2011 07:04 PM


The curved side pieces, not back, appear to be more artifice than anything
else, and could easily be replaced by two straight V cuts, its not critical.

rgds, sreten.

If I was building it I'd modify it for tapered expansion, looks crude to me.

highfieldrebel 10th October 2011 07:19 PM

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Despite Scott hating them, I used pocket screws for the construction, from a company called Kreg, check youtube for their videos. You must consider whether you want them visible afterwards, I had them internal except for the top and bottom pieces.

planet10 10th October 2011 07:20 PM

Keep the pictures coming :)


planet10 10th October 2011 07:23 PM


Originally Posted by sreten (
The curved side pieces, not back, appear to be more artifice than anything
else, and could easily be replaced by two straight V cuts, its not critical.

Actually they are not. Ron Clarke brought this design element to horns. It helps the wavefront coming out of a high aspect ratio rectangular horn mouth more easily approach the optimal spherical shape.


highfieldrebel 10th October 2011 07:25 PM

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At this stage of the project I have to say that it looks like a piece of art to me, hats off Scott, I didn't want to put the second side on, the cut edge of the BB looks lovely.

highfieldrebel 10th October 2011 07:29 PM

OK next to my least favourite part of the construction path I chose.

Once the internal parts are in and dried, you must check that the back and the two inner layers are at the same height, preferably the middle piece slightly higher, sand down as appropriate. Then glue up and attach the second side piece. This is the part of the build that was least satisfying as I couldn't check the fit of the hidden internal layer, maybe there was a gap? I did a 'damp' run by applying dabs of glue all along this piece and putting it together then checking was the glue squashed. It should have been ok but I still don't like it. ArtsyAllen used box joints in his built so he could know things were ok. Also, the screws do shift the wood a little, it's a small amount but visible. And worrying.

highfieldrebel 10th October 2011 07:34 PM

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OK from here it's plain sailing.... or should have been. Route out the rebates for the driver, only make sure you use the dimensions for the 10.2 driver, not the gen 1 driver, I know this idiot who .... where's the smilie for punching myself in the face?

Line the inside of the compression chamber with damping material, I couldn't get anything from the car stores so I bought some online, it was adhesive backed so it was super simple to insert.

Then glue the front on and wait.

6L6 10th October 2011 07:39 PM

Very nice! Your project seems to be progressing well.
As others have said, more photos please! Those you have posted so far are great.

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